// class method of mzhttpd

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <sys/stat.h>
#include <pthread.h>   // use multithreading
#include <sys/wait.h>
#include <stdlib.h>

#define ISspace(x) isspace((int)(x))

#define SERVER_STRING "Server: Mz1httpd/0.0.2\r\n"

#include "mzroute.h"
#include "mzhttp.h"   // define the basic http data struct

#include "utils/MzType2Mime.h"

#include "Mzhttpd.h"

Mzhttpd::Mzhttpd(){
	printf("@ Mz1httpd - mzi_mzi@163.com \n");
	printf("@ Create Mzhttpd on port: 80 \n");
	//default 80
	this->port = 80;
}
Mzhttpd::Mzhttpd(u_short port){
	printf("@ Mz1httpd - mzi_mzi@163.com \n");
	printf("@ Create Mzhttpd on port: %d \n", port);
	this->port = port;
	

}

Mzhttpd::~Mzhttpd(){
	printf("@Thanks for using Mzhttpd \n");
}



void Mzhttpd::run(){
	printf("mzhttpd server start to run! \n");
	
	int server_sock = -1;
	int client_sock = -1;
	//sockaddr_in 是 IPV4的套接字地址结构。定义在<netinet/in.h>,参读《TLPI》P1202
	struct sockaddr_in client_name;
	unsigned int client_name_len = sizeof(client_name); 
	
	pthread_t newthread;   // new thread id

	server_sock = this->startup();            // init
	printf("start up ok! on port: %d \n", this->port);


	while (1)
	{
		//阻塞等待客户端的连接，参读《TLPI》P1157
		client_sock = accept(server_sock,
                       (struct sockaddr *)&client_name,
                       &client_name_len);
		if (client_sock == -1)
			error_die("accept");

		  
		  // use main thread to handle(not good)
		  // accept_request(&client_sock);                 // handle an request
		
		// use anthor thread to handle
		// printf("> try to create thread \n");		
		// the fourth args don't use pointer, just pass value(important)
		if (pthread_create(&newthread , NULL, (void* (*)(void*))Mzhttpd::accept_request, (void*)client_sock) != 0){
			error_die("pthread_create");
		}else{
			// printf("> create success: %ld \n", newthread);
		}
		
	}

	close(server_sock);

}


/**********************************************************************/
/* A request has caused a call to accept() on the server port to
 * return.  Process the request appropriately.
 * Parameters: the socket connected to the client */
/**********************************************************************/
// static
void* Mzhttpd::accept_request(int _client)
{
	int client = _client;
 char buf[1024];
 int numchars;
 char method[255];
 char url[255];
 char path[512];
 size_t i, j;
 struct stat st;
 
 /*
 int cgi = 0;     // becomes true if server decides this is a CGI
                    
                    */
 char *query_string = NULL;

 // use mz_http_headers to format the request
 mz_http_headers headers;
 

 //读http 请求的第一行数据（request line），把请求方法存进 method 中
 numchars = get_line(client, buf, sizeof(buf));
 i = 0; j = 0;
 while (!ISspace(buf[j]) && (i < sizeof(method) - 1))
 {
  method[i] = buf[j];
  i++; j++;
 }
 method[i] = '\0';

 //如果请求的方法不是 GET 或 POST 任意一个的话就直接发送 response 告诉客户端没实现该方法
 if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
 {
	printf(" > @Mzhttpd::accept_request: 501: method: [%s] thread id:[%ld] \n", method, pthread_self());
	unimplemented(client);
	return NULL;
 }

	/*
 //如果是 POST 方法就将 cgi 标志变量置一(true)
 if (strcasecmp(method, "POST") == 0)
  cgi = 1;
  */

 i = 0;
 //跳过所有的空白字符(空格)
 while (ISspace(buf[j]) && (j < sizeof(buf))) 
  j++;
 
 //然后把 URL 读出来放到 url 数组中
 while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf)))
 {
  url[i] = buf[j];
  i++; j++;
 }
 url[i] = '\0';

 
	i = 0;
	char version[255];
	// jump over space
	while (ISspace(buf[j]) && (j < sizeof(buf))) 
		j++;

	// fetch version
	while (!ISspace(buf[j]) && (i < sizeof(version) - 1) && (j < sizeof(buf)))
	{
		version[i] = buf[j];
		i++; j++;
	}
	version[i] = '\0';
  
	// format args from url
	query_string = url;
	while ((*query_string != '?') && (*query_string != '\0')){ // to find '?'
		query_string++;
	}
	if (*query_string == '?'){
		// found query string
		// split url into two strings
		*query_string = '\0';
		query_string ++;         // point to next char
		// cgi = 1;         // use cgi(deprecated)
	}
	
	// format args into headers.args
	format_args(query_string, &headers.args);
	
	// save data into mz_http_headers
	strcpy(headers.method, method);
	strcpy(headers.url, url);
	strcpy(headers.version, version);
	headers.query_string = query_string;        // temporary

	// for test and debug
	show_headers(&headers);

	// start try route
	long func = serve(url);
	if(func != 0){
		// call func
		char*(*p)(mz_http_headers*);
		p = (char*(*)(mz_http_headers*))func;
	    char* buf = (*p)(&headers);  // call
		printf("ret: %s \n", buf);
		serve_route(client, buf);      // send response
		free(buf);                   // free char* buf from the callback function
		delete_mz_args(&headers.args);   // free
		close(client);
		return NULL;         // close socket and return
	}
	delete_mz_args(&headers.args);   // free


 //将前面分隔两份的前面那份字符串，拼接在字符串htdocs的后面之后就输出存储到数组 path 中。相当于现在 path 中存储着一个字符串
 sprintf(path, "htdocs%s", url);
 
 //如果 path 数组中的这个字符串的最后一个字符是以字符 / 结尾的话，就拼接上一个"index.html"的字符串。首页的意思
 if (path[strlen(path) - 1] == '/')
  strcat(path, "index.html");
 
 //在系统上去查询该文件是否存在
 if (stat(path, &st) == -1) {
  //如果不存在，那把这次 http 的请求后续的内容(head 和 body)全部读完并忽略
  while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
   numchars = get_line(client, buf, sizeof(buf));
  //然后返回一个找不到文件的 response 给客户端
  not_found(client);
 }
 else
 {
  //文件存在，那去跟常量S_IFMT相与，相与之后的值可以用来判断该文件是什么类型的
  //S_IFMT参读《TLPI》P281，与下面的三个常量一样是包含在<sys/stat.h>
  if ((st.st_mode & S_IFMT) == S_IFDIR)  
   //如果这个文件是个目录，那就需要再在 path 后面拼接一个"/index.html"的字符串
   strcat(path, "/index.html");
   
	serve_file(client, path);    // delete cgi
	
   /*
   //S_IXUSR, S_IXGRP, S_IXOTH三者可以参读《TLPI》P295
  if ((st.st_mode & S_IXUSR) ||       
      (st.st_mode & S_IXGRP) ||
      (st.st_mode & S_IXOTH)    )
   //如果这个文件是一个可执行文件，不论是属于用户/组/其他这三者类型的，就将 cgi 标志变量置一
   cgi = 1;
   
  if (!cgi)
   //如果不需要 cgi 机制的话，
   serve_file(client, path);
  else
   //如果需要则调用
   execute_cgi(client, path, method, query_string);
 
 */
	}
 close(client);
 return NULL;
}


/**********************************************************************/
/* Inform the client that a request it has made has a problem.
 * Parameters: client socket */
/**********************************************************************/
void Mzhttpd::bad_request(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "Content-type: text/html\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "<P>Your browser sent a bad request, ");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "such as a POST without a Content-Length.\r\n");
 send(client, buf, sizeof(buf), 0);
}


/**********************************************************************/
/* Put the entire contents of a file out on a socket.  This function
 * is named after the UNIX "cat" command, because it might have been
 * easier just to do something like pipe, fork, and exec("cat").
 * Parameters: the client socket descriptor
 *             FILE pointer for the file to cat */
/**********************************************************************/

/*
Mz1: things from the origin project is wrong here, it won't send the last buf
	and now I fix it.
	also '\0' won't be send properly.

*/
void Mzhttpd::cat(int client, FILE *resource)
{
 char buf[1024];
	size_t _size = 0;

 //从文件文件描述符中读取指定内容
 // fgets(buf, sizeof(buf), resource);
 _size = fread(buf, 1, sizeof(buf), resource);       // change to use fread
 while (!feof(resource))
 {
  send(client, buf, _size, 0);
  // fgets(buf, sizeof(buf), resource);
  _size = fread(buf, 1, sizeof(buf), resource);       // change to use fread
  
  // debug
  // printf(" > @ Mzhttpd::cat : _size: %ld \n", _size);
 }
 send(client, buf, _size, 0);        // send the last buf

}



/**********************************************************************/
/* Inform the client that a CGI script could not be executed.
 * Parameter: the client socket descriptor. */
/**********************************************************************/
void Mzhttpd::cannot_execute(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<P>Error prohibited CGI execution.\r\n");
 send(client, buf, strlen(buf), 0);
}


/**********************************************************************/
/* Print out an error message with perror() (for system errors; based
 * on value of errno, which indicates system call errors) and exit the
 * program indicating an error. */
/**********************************************************************/
void Mzhttpd::error_die(const char *sc)
{
 //包含于<stdio.h>,基于当前的 errno 值，在标准错误上产生一条错误消息。参考《TLPI》P49
 perror(sc); 
 exit(1);
}


/**********************************************************************/
/* Execute a CGI script.  Will need to set environment variables as
 * appropriate.
 * Parameters: client socket descriptor
 *             path to the CGI script */
/**********************************************************************/
void Mzhttpd::execute_cgi(int client, const char *path,
                 const char *method, const char *query_string)
{
 char buf[1024];
 int cgi_output[2];
 int cgi_input[2];
 pid_t pid;
 int status;
 int i;
 char c;
 int numchars = 1;
 int content_length = -1;
 
 //往 buf 中填东西以保证能进入下面的 while
 buf[0] = 'A'; buf[1] = '\0';
 //如果是 http 请求是 GET 方法的话读取并忽略请求剩下的内容
 if (strcasecmp(method, "GET") == 0)
  while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
   numchars = get_line(client, buf, sizeof(buf));
 else    /* POST */
 {
  //只有 POST 方法才继续读内容
  numchars = get_line(client, buf, sizeof(buf));
  //这个循环的目的是读出指示 body 长度大小的参数，并记录 body 的长度大小。其余的 header 里面的参数一律忽略
  //注意这里只读完 header 的内容，body 的内容没有读
  while ((numchars > 0) && strcmp("\n", buf))
  {
   buf[15] = '\0';
   if (strcasecmp(buf, "Content-Length:") == 0)
    content_length = atoi(&(buf[16])); //记录 body 的长度大小
   numchars = get_line(client, buf, sizeof(buf));
  }
  
  //如果 http 请求的 header 没有指示 body 长度大小的参数，则报错返回
  if (content_length == -1) {
   bad_request(client);
   return;
  }
 }

 sprintf(buf, "HTTP/1.0 200 OK\r\n");
 send(client, buf, strlen(buf), 0);

 //下面这里创建两个管道，用于两个进程间通信
 if (pipe(cgi_output) < 0) {
  cannot_execute(client);
  return;
 }
 if (pipe(cgi_input) < 0) {
  cannot_execute(client);
  return;
 }

 //创建一个子进程
 if ( (pid = fork()) < 0 ) {
  cannot_execute(client);
  return;
 }
 
 //子进程用来执行 cgi 脚本
 if (pid == 0)  /* child: CGI script */
 {
  char meth_env[255];
  char query_env[255];
  char length_env[255];

  //dup2()包含<unistd.h>中，参读《TLPI》P97
  //将子进程的输出由标准输出重定向到 cgi_ouput 的管道写端上
  dup2(cgi_output[1], 1);
  //将子进程的输出由标准输入重定向到 cgi_ouput 的管道读端上
  dup2(cgi_input[0], 0);
  //关闭 cgi_ouput 管道的读端与cgi_input 管道的写端
  close(cgi_output[0]);
  close(cgi_input[1]);
  
  //构造一个环境变量
  sprintf(meth_env, "REQUEST_METHOD=%s", method);
  //putenv()包含于<stdlib.h>中，参读《TLPI》P128
  //将这个环境变量加进子进程的运行环境中
  putenv(meth_env);
  
  //根据http 请求的不同方法，构造并存储不同的环境变量
  if (strcasecmp(method, "GET") == 0) {
   sprintf(query_env, "QUERY_STRING=%s", query_string);
   putenv(query_env);
  }
  else {   /* POST */
   sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
   putenv(length_env);
  }
  
  //execl()包含于<unistd.h>中，参读《TLPI》P567
  //最后将子进程替换成另一个进程并执行 cgi 脚本
  execl(path, path, NULL);
  exit(0);
  
 } else {    /* parent */
  //父进程则关闭了 cgi_output管道的写端和 cgi_input 管道的读端
  close(cgi_output[1]);
  close(cgi_input[0]);
  
  //如果是 POST 方法的话就继续读 body 的内容，并写到 cgi_input 管道里让子进程去读
  if (strcasecmp(method, "POST") == 0)
   for (i = 0; i < content_length; i++) {
    recv(client, &c, 1, 0);
    write(cgi_input[1], &c, 1);
   }
   
  //然后从 cgi_output 管道中读子进程的输出，并发送到客户端去
  while (read(cgi_output[0], &c, 1) > 0)
   send(client, &c, 1, 0);

  //关闭管道
  close(cgi_output[0]);
  close(cgi_input[1]);
  //等待子进程的退出
  waitpid(pid, &status, 0);
 }
}


/**********************************************************************/
/* Get a line from a socket, whether the line ends in a newline,
 * carriage return, or a CRLF combination.  Terminates the string read
 * with a null character.  If no newline indicator is found before the
 * end of the buffer, the string is terminated with a null.  If any of
 * the above three line terminators is read, the last character of the
 * string will be a linefeed and the string will be terminated with a
 * null character.
 * Parameters: the socket descriptor
 *             the buffer to save the data in
 *             the size of the buffer
 * Returns: the number of bytes stored (excluding null) */
/**********************************************************************/
int Mzhttpd::get_line(int sock, char *buf, int size)
{
 int i = 0;
 char c = '\0';
 int n;

 while ((i < size - 1) && (c != '\n'))
 {
  //recv()包含于<sys/socket.h>,参读《TLPI》P1259, 
  //读一个字节的数据存放在 c 中
  n = recv(sock, &c, 1, 0);
  /* DEBUG printf("%02X\n", c); */
  if (n > 0)
  {
   if (c == '\r')
   {
    //
    n = recv(sock, &c, 1, MSG_PEEK);
    /* DEBUG printf("%02X\n", c); */
    if ((n > 0) && (c == '\n'))
     recv(sock, &c, 1, 0);
    else
     c = '\n';
   }
   buf[i] = c;
   i++;
  }
  else
   c = '\n';
 }
 buf[i] = '\0';

 return(i);
}


/**********************************************************************/
/* Return the informational HTTP headers about a file. */
/* Parameters: the socket to print the headers on
 *             the name of the file */
/**********************************************************************/
void Mzhttpd::headers(int client, const char *filename)
{
 char buf[1024];
 (void)filename;  /* could use filename to determine file type */

 strcpy(buf, "HTTP/1.0 200 OK\r\n");
 send(client, buf, strlen(buf), 0);
 strcpy(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 strcpy(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
}


/**********************************************************************/
/* Give a client a 404 not found status message. */
/**********************************************************************/
void Mzhttpd::not_found(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<BODY><P>The server could not fulfill\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "your request because the resource specified\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "is unavailable or nonexistent.\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</BODY></HTML>\r\n");
 send(client, buf, strlen(buf), 0);
}



// use this function to help serve_file
unsigned long Mzhttpd::get_file_size(const char *filename)  
{  
    struct stat buf;  
    if(stat(filename, &buf)<0)  
    {  
        return 0;  
    }  
    return (unsigned long)buf.st_size;  
}

void Mzhttpd::serve_file_headers(int client, const char *filename, unsigned long fsize)
{
 char buf[1024];
 int i;
 char ftype[255] = {0};
 MzType2Mime* dict;
 
 (void)filename;  /* could use filename to determine file type */

 strcpy(buf, "HTTP/1.0 200 OK\r\n");
 send(client, buf, strlen(buf), 0);
 strcpy(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 
	// add connection close
	strcpy(buf, "Connection: close\r\n");
	send(client, buf, strlen(buf), 0);

	// file type needs judge
	for (i = strlen(filename)-1; i>=0; i--){
		if (filename[i] == '.'){
			strcpy(ftype, &filename[i]);
			// printf(" > @Mzhttpd::serve_file_headers: file type: %s \n", &filename[i]);
			break;
		} 
	}
	// build a convertor
	dict = new MzType2Mime();
	char* mime = dict->get(ftype);
	if (mime){
		sprintf(buf, "Content-Type: %s\r\n", mime);
		printf(" > @Mzhttpd::serve_file_headers: Content-Type: %s\r\n", mime);
	}else{
		sprintf(buf, "Content-Type: text/plain\r\n");
	}
	delete dict; // free
	send(client, buf, strlen(buf), 0);
	
	sprintf(buf, "Content-Length: %ld\r\n", fsize);             // add size
	send(client, buf, strlen(buf), 0);
 strcpy(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
}


/**********************************************************************/
/* Send a regular file to the client.  Use headers, and report
 * errors to client if they occur.
 * Parameters: a pointer to a file structure produced from the socket
 *              file descriptor
 *             the name of the file to serve */
/**********************************************************************/
void Mzhttpd::serve_file(int client, const char *filename)
{
 FILE *resource = NULL;
 int numchars = 1;
 char buf[1024];

 //确保 buf 里面有东西，能进入下面的 while 循环
 buf[0] = 'A'; buf[1] = '\0';
 //循环作用是读取并忽略掉这个 http 请求后面的所有内容
 while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
  numchars = get_line(client, buf, sizeof(buf));

	// get file size 
	unsigned long fsize = get_file_size(filename);
	printf(" > FILE[%s] size: %ld \n", filename, fsize);
	
 //打开这个传进来的这个路径所指的文件
 resource = fopen(filename, "r");
 if (resource == NULL)
  not_found(client);
 else
 {
  //打开成功后，将这个文件的基本信息封装成 response 的头部(header)并返回
  serve_file_headers(client, filename, fsize);
  //接着把这个文件的内容读出来作为 response 的 body 发送到客户端
  cat(client, resource);
 }
 
 fclose(resource);
}


/**********************************************************************/
/* This function starts the process of listening for web connections
 * on a specified port.  If the port is 0, then dynamically allocate a
 * port and modify the original port variable to reflect the actual
 * port.
 * Parameters: pointer to variable containing the port to connect on
 * Returns: the socket */
/**********************************************************************/
int Mzhttpd::startup()
{
 int httpd = 0;
 //sockaddr_in 是 IPV4的套接字地址结构。定义在<netinet/in.h>,参读《TLPI》P1202
 struct sockaddr_in name;
 
 //socket()用于创建一个用于 socket 的描述符，函数包含于<sys/socket.h>。参读《TLPI》P1153
 //这里的PF_INET其实是与 AF_INET同义，具体可以参读《TLPI》P946
 httpd = socket(PF_INET, SOCK_STREAM, 0);
 if (httpd == -1)
  error_die("socket");
  
 memset(&name, 0, sizeof(name));
 name.sin_family = AF_INET;
 //htons()，ntohs() 和 htonl()包含于<arpa/inet.h>, 参读《TLPI》P1199
 //将*port 转换成以网络字节序表示的16位整数
 name.sin_port = htons(this->port);
 //INADDR_ANY是一个 IPV4通配地址的常量，包含于<netinet/in.h>
 //大多实现都将其定义成了0.0.0.0 参读《TLPI》P1187
 name.sin_addr.s_addr = htonl(INADDR_ANY);
 
 //bind()用于绑定地址与 socket。参读《TLPI》P1153
 //如果传进去的sockaddr结构中的 sin_port 指定为0，这时系统会选择一个临时的端口号
 if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
  error_die("bind");
  
 //如果调用 bind 后端口号仍然是0，则手动调用getsockname()获取端口号
 if (this->port == 0)  /* if dynamically allocating a port */
 {
  unsigned int namelen = sizeof(name);  // change to unsigned --mz
  //getsockname()包含于<sys/socker.h>中，参读《TLPI》P1263
  //调用getsockname()获取系统给 httpd 这个 socket 随机分配的端口号
  if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
   error_die("getsockname");
  this->port = ntohs(name.sin_port);
 }
 
 //最初的 BSD socket 实现中，backlog 的上限是5.参读《TLPI》P1156
 // if (listen(httpd, 5) < 0) 
	if (listen(httpd, 20) < 0) {             // more listen!
		error_die("listen");
	}
 return(httpd);
}



/**********************************************************************/
/* Inform the client that the requested web method has not been
 * implemented.
 * Parameter: the client socket */
/**********************************************************************/
void Mzhttpd::unimplemented(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</TITLE></HEAD>\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</BODY></HTML>\r\n");
 send(client, buf, strlen(buf), 0);
}

// mzroute
void Mzhttpd::serve_route(int client, const char* buf){
  int numchars = 1;
  char _buf[1024];
 
  //确保 _buf 里面有东西，能进入下面的 while 循环
  _buf[0] = 'A'; _buf[1] = '\0';
  //循环作用是读取并忽略掉这个 http 请求后面的所有内容
  while ((numchars > 0) && strcmp("\n", _buf))  /* read & discard heade    rs */
   numchars = get_line(client, _buf, sizeof(_buf));

 headers(client, NULL);
 send(client, buf, strlen(buf), 0);
 send(client, "\r\n", 2, 0);
}
























